Vacuum pump designed as displacement pump

ABSTRACT

In a vacuum pump designed as a displacement pump for drawing off vapor-containing gases and having a discharge point communicating with a storage vessel having an outlet aperture for the pumped gases and containing a supply of sealing fluid covering a discharge valve, heating means are provided to heat at least that portion of the wall of the storage vessel located above the level of the sealing fluid therein. The heating means may include a double jacket heated by a through-flowing heating medium, or may be an electric heating jacket surrounding the upper portion of the storage vessel. A line may be provided to return sealing fluid from the storage vessel into the pump, this line being in heat-conducting relation with that portion of the vessel wall located above the fluid level.

United States Patent Kohler Feb. 22, 1972 [54] VACUUM PUMP DESIGNED AS [56] References Cited DISPLACEMENT PUMP UNITED STATES PATENTS 1 lnvenwfl Marcel Kohl", Ballets, Liwhtenstein 3,310,229 3/1967 Maehara ..41s/ss I [73] Assignee: Balzers latent-und Beteiligung Akfl 1,029,309 6/1912 M1les ..4l8/85 X gesellsch ft, B z Li in Primary Examiner-C. L. Albritton [22] Filed: Man 27, 1970 Attorney-McGlew and Toren 211 App]. No.: 22,580 [57] ABSTRACT In a vacuum pump designed as a displacement pump for drawing ofi' vapor-containing gases and having a discharge point communicating with a storage vessel having an outlet aperture [30] Fore'gn Apphcatlon Monty Data for the pumped gases and containing a supply of sealing fluid Mar. 31, 1969 Germany ..P 19 16 394.1 covering a discharge valve, heating means are Provided to heat at least that portion of the wall of the storage vessel located above the level of the sealing fluid therein. The heating means may include a double jacket heated by a through- [52] 11.8. CI ..219/201, 418/85, fills/2959; flowing heating medium or may be an eiectric heatingjacket [51] Intel. H05) 1/00 surrounding the upper portion of the storage vessel. A line [58] Field 8/80 97 may be provided to return sealing fluid from the storage vessel I 2118/99 5 into the pump, this line being in heat-conducting relation with that portion of the vessel wall located above the fluid level.

5 Claims, 1 Drawing Figure VACUUM PUMP DESIGNED AS DISPLACEMENT PUMP BACKGROUND OF THE INVENTION This invention relates to vacuum pumps designed as displacement pumps and which draw in, compress and then eject the gas to be delivered, by periodic enlargement and reduction of a workspace defined by solid structural elements, such as pistons, rotors, slides, valves, etc. Such pumps are known to have the disadvantage that, in the removal of the vapors, due to the compression, condensates are formed, and these get into the sealing fluid and thereby greatly reduce the attainable vacuum.

It is known to prevent formation of a condensate by heating the entire pump above the boiling point of the vapors to be removed and at atmospheric pressure. Such a heated pump is suitable preferably for the extraction of steam. However, if the problem is to remove vapors containing substances which attack the material of the pump, the chemical reaction rate can increase so greatly, with relatively little heating, that the packing surfaces of the pump are damaged, in a short time, to an extent such that the pump becomes unserviceable. In addition, for certain va'pors, very high heating temperatures would have to be employed to counter liquefaction effectively. In order that the sealing fluid of a heated pump will have a sufficient lubricating effect at the high operating temperatures, it must have a high viscosity at room temperature. However, this results in difficulties in starting such a pump, unless it is preheated, and this would involve considerable extra expense and loss of time.

German Pat. No. 702,480 discloses an arrangement for preventing the condensation of vapors in a vacuum pump, for producing high vacuums, by introducing a certain quantity of gas, in particular air, at a point of the pump space blocked off from the suction line, and where the quantity of gas admixed with the vapor is proportioned so that the formation of liquid in the pump, due to liquefaction of the vapors drawn off, is either prevented or at least reduced to an innocuous degree.

This known so-called gas ballast pump" is limited in its ability to pump off vapors in continuous operation. At higher suction pressures of the gases to be pumped off, in fact, it is not sufficiently capable of taking up the ballast gases. The provision of a gas ballast valve, which, with a greater flow passage cross section and if arranged at a suitable point in the pump, should bring about the admission of more than the usual quantity of ballast gas, fails due to the fact that, at the high speeds required for rotary displacement pumps to attain suction capacities of great volume, the time span available for the introduction of the ballast gas, during which the ballast gas inlet is in communication with a selected pump chamber, is too short.

It has also been proposed, to introduce a sufficient quantity of ballast gas, to introduce the latter under increased pressure or at several points, for example, into the compression zone and into the connecting line between two stages of a two-stage pump. All these known measures have resulted in an improvement, but the danger of condensate formation still has not been reliably eliminated in many cases where relatively large quantities of vapor are produced.

SUMMARY OF THE INVENTION The objective of the present invention is to improve the ability to remove vapors from vacuum pumps, designed as displacement pumps and which are equipped with known means or other means for preventing condensation of vapors in the interior of the pump, and whose discharge port communicates with a storage vessel provided with an outlet aperture for the pumped gases and containing a supply of sealing fluid covering the discharge valve of the pump. In accordance with the present invention, at least that portion of the storage vessel wall located above the level of the sealing fluid therein is heatable.

With the solution to the problem proposed by the present invention, it is possible to get along with a moderate heating of the pump chamber, with a relatively small quantity of ballast gas, or with both. Usually the temperature in the interior of the pump is sufficient, this temperature being present on the inner wall without additional heating and being due solely to the friction of the moving pump parts.

The effect of the solution proposed by the invention may be understood from the following. It has been surprising to note that the contamination of the sealing fluid with vapor condensates does not arise primarily from the fact that the condensation of the vapors in the pump chambers cannot be suppressed with known means. What has been overlooked, up to the present time, is that the vapors delivered by the pump, after passing through the sealing fluid supply above the discharge valve, can condense at those portions of the inner wall of the storage vessel not covered by the hot sealing fluid, because these wall portions usually have too low a temperature. The condensate formed at these wall portions drips or trickles from the wall, and thus enters into the sealing fluid, becomes mixed with the latter and thereby returns into the pump. By heating these wall portions, condensation is prevented in a known manner, and it is thereby assured that the gas-vapor mixture delivered by the pump leaves the vessel through the outlet aperturewithout being able to do any damage.

An object of the invention is to provide an improved vacuum pump designed as a displacement pump.

An other object of the invention is to provide such a vacuum pump including improved means for preventing the formation of condensate when the pump is used to pump vapor-containing gases.

A further object of the invention is to provide such a pump including a storage vessel communicating with the discharge port of the pump and containing a sealing fluid for a discharge valve, and in which at least those portions of the walls of the storage vessel above the level of the sealing fluid therein are heated.

For an understanding of the principles of the invention, reference is made to the following description of a typical embodiment thereof as illustrated in the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING In the drawing, the single FIGURE is a substantially diametric sectional view through a vacuum pump embodying the invention. 1

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, a rotary vane type vacuum pump is illustrated as including a housing 1 in which is rotatably and eccentrically mounted a rotor 2 formed with radial slots receiving radially displaceable vanes 3. Springs 4 bias vanes 3 against the inner wall or surface of the pump housing, and divide the housing into several pump chambers. The vapor-containing gas to be pumped is drawn in through an inlet line 5,

, compressed by rotation of rotor 2 in the direction indicated by the arrow, and finally ejected through the discharge valve 6 into the storage vessel 7 for the sealing fluid. The vapor-containing gas rises through the sealing fluid into the space 8 in vessel 7 above the sealing fluid, and then flows out through outlet aperture 9.

The rotary vane pump, as so far described, is an ordinary vacuum pump. In accordance with the invention, means are provided for heating the wall portion 9 of vessel 7 located above the sealing fluid, wall portion 9' in the illustrated example being designed as ajacket 10 which is traversed by a heating medium. It is especially expedient to use the hot sealing fluid itself as a heating medium, and to return it through the heating jacket to the discharge space of the pump through line 11, as illustrated in the drawing.

However, in place of this type of wall heating, or in addition thereto, an electrical heating jacket 12, surrounding at least the upper portion of storage vessel 7, may be provided. In the latter case, there is the advantage that not only the wall of vessel 7 is heated, as desired, but at the same time the sealing fluid returns to the pumps at an increased temperature, thus helping to maintain the temperature of the pump chambers high enough to avoid condensation. This method of heating the pump chambers is technically simpler and more economical than the known procedure of immersing the entire pump housing in a heating bath, or enveloping the entire pump with other heat-supplying media or means.

Particularly in the case of high-speed pumps, on the other hand, it may be expedient to cool the sealing fluid returned from storage vessel 7 through line 11, by means of a cooling device inserted in line 11.

The solution to the problem of vapor condensation, in accordance with the invention, is useful in connection with any known method for the suppression of vapor condensation in the interior of a pump, that is, both in connection with pumps where the entire pump housing is heated and in connection with gas ballast pumps, as well as in connection with pumps where both measures are used simultaneously, These additional auxiliary devices form no part of the present invention, and consequently have not been shown in the drawing.

While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

1. In a vacuum pump designed as a displacement pump for drawing off vapor-containing gases and including a pump housing wall having a discharge port communicating with a walled storage vessel having an outlet aperture for the pumped gases and containing a supply of sealing fluid partly filling said vessel and covering a discharge valve in the discharge port, the improvement comprising heating means operable to heat at least that portion of the vessel wall located above the level of the sealing fluid in said vessel.

2. in a vacuum pump, the improvement claimed in claim 1, including a line for the return of sealing fluid from said storage vessel into said pump, said line being connected, for heat conduction, with that portion of the storage vessel wall located above thesealing fluid level therein.

3. In a vacuum pump designed as a displacement pump for drawing off vapor-containing gases and including a pump housing wall having a discharge port communicating with a walled storage vessel having an outlet aperture for the pumped gases and containing a supply of sealing fluid covering a discharge valve in the discharge port, the improvement comprising heating means operable to heat at least that portion of the vessel wall located above the level of the sealing fluid in said vessel; that portion of the vessel wall located above the sealing fluid level being formed as a double jacket heatable by a through-flowing heating medium.

4. In a vacuum pump designed as a displacement pump for drawing off vapor-containing gases and including a pump housing wall having a discharge port communicating with a walled storage vessel having an outlet aperture for the pumped gases and containing a supply of sealing fluid covering a discharge valve in the discharge port, the improvement comprising heating means operable to heat at least that portion of the vessel wall located above the level of the sealing fluid in said vessel; said heating means including electric heating means surrounding at least that portion of the vessel wall located above the sealing fluid level.

4. In a vacuum pump, the improvement claimed in claim 4, in which said electric heating means is an electric heating jacket. 

1. In a vacuum pump designed as a displacement pump for drawing off vapor-containing gases and including a pump housing wall having a discharge port communicating with a walled storage vessel having an outlet aperture for the pumped gases and containing a supply of sealing fluid partly filling said vessel and covering a discharge valve in the discharge port, the improvement comprising heating means operable to heat at least that portion of the vessel wall located above the level of the sealing fluid in said vessel.
 2. In a vacuum pump, the improvement claimed in claim 1, including a line for the return of sealing fluid from said storage vessel into said pump, said line being connected, for heat conduction, with that portion of the storage vessel wall located above the sealing fluid level therein.
 3. In a vacuum pump designed as a displacement pump for drawing off vapor-containing gases and including a pump housing wall having a discharge port communicating with a walled storage vessel having an outlet aperture for the pumped gases and containing a supply of sealing fluid covering a discharge valve in the discharge port, the improvement comprising heating means operable to heat at least that portion of the vessel wall located above the level of the sealing fluid in said vessel; that portion of the vessel wall located above the sealing fluid level being formed as a double jacket heatable by a through-flowing heating medium.
 4. In a vacuum pump designed as a displacement pump for drawing off vapor-containing gases and including a pump housing wall having a discharge port communicating with a walled storage vessel having an outlet aperture for the pumped gases and containing a supply of sealing fluid covering a discharge valve in the discharge port, the improvement comprising heating means operable to heat at least that portion of the vessel wall located above the level of the sealing fluid in said vessel; said heating means including electric heating means surrounding at least that portion of the vessel wall located above the sealing fluid level.
 4. In a vacuum pump, the improvement claimed in claim 4, in which said electric heating means is an electric heating jacket. 